Internal combustion engines in vehicles may be subject to a wide range of operating conditions and fuels. The operating conditions may increase or decrease fuel vaporization within the engine, thereby making it more difficult to start and operate the engine. Further, different fuel distributors may supply fuels that have higher or lower volatility than fuels supplied by other fuel distributors. The volatility of the fuel may also make starting the engine more difficult. One consequence of operating the engine over a wide range of conditions with varying fuel types is engine misfire. An air-fuel mixture introduced to the cylinder may not combust or may partially combust as a result of low fuel volatility during colder temperatures. In some engines, injected fuel amount, spark timing, and/or the effective compression ratio may be adjusted to improve the possibility of combusting the air-fuel mixture and reducing misfire. However, it may not be desirable to adjust an amount of fuel supplied to an engine, engine spark timing, or effective compression ratio unless misfire is detected.
Engine misfire may be detected by monitoring engine speed. If an air-fuel mixture in a cylinder does not combust or partially combusts, engine torque may be reduced. As a result, engine speed may decline for at least a portion of an engine cycle. However, changes in engine speed related to misfire may be less noticeable for engines having a higher number of cylinders. For example, it may be more difficult to detect a misfire of an eight cylinder engine as compared to a four cylinder engine. Additionally, it may be more difficult to detect a misfire at higher engine speeds since engine combustion events are spaced closer together in time.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: adjusting an actuator to adjust a pressure in a cylinder in response to a position of a waste gate during a blow-down portion of a cycle of the cylinder.
Engine misfire may be determined from a position of a turbocharger waste gate and/or an amount of current supplied to a waste gate actuator to control position of the turbocharger waste gate. In particular, pressure from a combusted mixture increases pressure in the exhaust manifold when exhaust is released from a cylinder via opening a cylinder exhaust valve. The increased exhaust manifold pressure can exert force on a turbocharger waste gate causing the position of the waste gate to deflect from a desired position. The deflection of the waste gate may be indicative of a misfire. For example, a cylinder combusting an air-fuel mixture may generate a first pressure in a cylinder when the air-fuel mixture completely combusts. On the other hand, an equivalent air-fuel mixture may generate a second, lower pressure, when the air-fuel mixture is only partially combusted. Thus, the waste gate position may change by a greater amount from a desired position when the air-fuel mixture is completely combusted and released from the cylinder to the exhaust manifold. As such, the waste gate position may be a good indicator of whether or not misfire occurs in an engine cylinder. And, once misfire is detected, cylinder pressure may be increased by adjusting an actuator that reduces the possibility of misfire.
The present description may provide several advantages. Specifically, the approach may provide a reliable way to determine engine misfire in turbocharged engines. Additionally, the approach may provide a cross-check to other misfire detection methods such as misfire detection using engine speed. Further, the approach may be more reliable than other engine misfire detection schemes during particular engine operating conditions, such as during engine starting.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.